This invention relates to a device for transferring high energy electromagnetic radiation from a laser source to an optical fiber, said device being in the form of an integral optical fiber coupler.
The device of the invention is particularly adapted to be used in apparatus for directing laser radiation on to targets such as vascular obstructions and atherosclerotic lesions.
The common disease atherosclerosis, which is a type of arteriosclerosis, is characterized by the formation of atherosclerotic lesions (also known as atherosclerotic plaques) on the inner wall of the aorta and the large and medium-sized arteries. The most important symptom in the early stages of this disease can lead to total blood vessel blockage, and ultimately, death of the patient. The atherosclerotic lesions are masses of fatty material associated with fibrous connective tissue, very often with secondary deposits of calcium salts and blood constituents. Human atherosclerotic lesions are characterized by a large lipid content, which may account for as much as 60 percent of the dry weight of some advanced lesions. Three major classes of lipids are found, i.e. cholesterol, cholesterol esters and phospholipids.
One technique currently practiced for correcting problems arising from arteriosclerotic lesions is coronary or peripheral arterial bypass surgery, in which a blood vessel segment removed from another part of the patient's body, e.g. a saphenous vein segment, or a synthetic vascular graft is implanted in parallel with the occluded artery. Although arterial bypass surgery has been practiced with great success for many years, it is a major surgical operation with inevitable attendant risks and the medical profession therefore has continued to search for techniques for reducing vascular obstructions such as arteriosclerotic lesions without bypass surgery.
Another technique currently practiced with considerable success in the treatment of arteriosclerosis is transluminal angioplasty, in which a balloon catheter is inserted into an affected blood vessel and the balloon then expanded outwardly against the occlusion to recannulate the vessel. One disadvantage of this technique is that it cannot be employed when the vessel is already fully blocked (or almost so) by occlusions. Also, it results principally in redistribution (i.e. compaction) rather than physical or chemical removal of the lesion material, most of which remains in the affected blood vessel wall and can serve as a site for future occlusive growth.
Recently it has been proposed to reduce vascular occlusions such as arteriosclerotic lesions by laser revascularization, in which electromagnetic radiation generated by a laser is carried by one or more optical fibers to the vicinity of the occlusion and directed at the occlusion. Uptake of the laser radiation by occlusion materials results in its conversion to relatively low molecular weight organic substances, which are dissolved in and carried away by the blood stream. Examples of apparatus for the practice of laser revascularization are disclosed in U.S. Pat. No. 4,207,874; U.S. Pat. No. 4,418,688; World Published patent application 8301893, published June 9, 1983; World Published application No. 8303188, published Sept. 29, 1983 and World Published patent application No. 8302885, published Sept. 1, 1983. A significant advantage of laser revascularization is that it can result in the essentially complete removal of a vascular occlusion (e.g. an arteriosclerotic lesion) in a surgical procedure that is far less invasive than bypass surgery. However, because of the difficulty in designing a laser catheter system whose use assures that the laser beam is carefully directed to impinge only upon the undesired occlusion, the practice of this technique involves a risk of damage to blood constituents and healthy surrounding tissues, particularly the surrounding non-arteriosclerotic blood vessel tissue.
Commonly assigned patent application Ser. No. 573,448 discloses a method for the reduction of an arteriosclerotic lesion without significant risk of damage to surrounding blood and healthy tissues involving the use of electromagnetic radiation in which substantially all of the electromagnetic radiation directed at the lesion is of a wavelength in the ultraviolet or visible region at which energy is selectively absorbed, as compared to absorption by whole blood and non-arteriosclerotic blood vessel tissue, by a lesion component present in said lesion at a greater weight percentage (on a dry basis) than in the whole blood or surrounding non-arteriosclerotic blood vessel tissue of the patient. The ensuing reaction and decomposition of said lesion component leads directly to the reduction of the lesion without significant risk to damage of the vicinal blood or, should the electromagnetic radiation be inadvertently misdirected, to the surounding healthy tissues. The electromagnetic radiation directed at the lesion is preferably monochromatic, i.e. substantially all within an extremely narow wavelength range. Preferably monochromatic electromagnetic radiation is generated by a laser and conducted to the vicinity of the lesion by at least one optical fiber. Monochromatic ultraviolet energy is preferably generated by an excimer laser.
Thus, cholesterol, which is a common component of arteriosclerotic lesions, selectively absorbs electromagnetic radiation having a wavelength of about 248 nanometers and treatment as described above with laser radiation of said wavelength leads to reduction of the lesion.
As used herein, the term "reducing an arteriosclerotic lesion", or the like, means substantially reducing the size of the lesion. Preferably, treatment is continued until essentially complete removal of the lesion has been achieved.
The use of electromagnetic radiation of a particular wavelength to selectively reduce or obliterate arteriosclerotic lesions does not depend upon the use of a particular delivery system but only upon the use of the type of radiation. However, without the use of a coupler system such as the one described herein the efficiency of the energy transfer from the laser to the optical fiber is greatly reduced.
It has now been found that the operation of a system using a laser source of electromagnetic radiation and directing said radiation to a target through one or more optical fibers is significantly improved and degradation of the optical fiber is reduced if the radiation from the laser to the optical fiber is conveyed through a coupling device, more particularly an integral optical fiber coupler.